ALBERT

Description: Bortezomib (BTZ) was recently evaluated in a randomized Phase 3 clinical trial which compared standard chemotherapy (cytarabine, daunorubicin, etoposide; ADE) to standard therapy with BTZ (ADEB) for de novo pediatric acute myeloid leukemia. While the study concluded that BTZ did not improve outcome overall, we examined patient subgroups benefitting from BTZ-containing chemotherapy using proteomic analyses. The proteasome inhibitor BTZ disrupts protein homeostasis and activates cytoprotective heat shock responses. We measured total heat shock factor 1 (HSF1) and phosphorylated HSF1 (HSF1-pSer326) in leukemic cells from 483 pediatric patients using Reverse Phase Protein Arrays. HSF1-pSer326 phosphorylation was significantly lower in pediatric AML compared to CD34+ non-malignant cells. We identified a strong correlation between HSF1-pSer326 expression and BTZ sensitivity. BTZ significantly improved outcome of patients with low-HSF1-pSer326 with a 5-year event-free survival of 44% (ADE) vs. 67% for low-HSF1-pSer326 treated with ADEB (P=0.019). To determine the effect of HSF1 expression on BTZ potency in vitro, cell viability with HSF1 gene variants that mimicked phosphorylated (S326A) and non-phosphorylated (S326E) HSF1-pSer326 were examined. Those with increased HSF1 phosphorylation showed clear resistance to BTZ vs. those with wild type or reduced HSF1-phosphorylation. We hypothesize that HSF1-pSer326 expression could identify patients that benefit from BTZ-containing chemotherapy.

Description: Our group and others have shown that acute myeloid leukemia (AML) cells have unique mitochondrial characteristics with an increased reliance on oxidative phosphorylation. Through an shRNA screen for new biological vulnerabilities in the mitochondria of AML cells, we identified the mitochondrial protease, neurolysin (NLN). NLN is a zinc metalloprotease whose mitochondrial function is not well understood and whose role in AML growth and viability has not been previously reported. We analyzed the expression of NLN in AML cells and normal hematopoietic cells. By immunoblotting, NLN was overexpressed in 80% of primary AML patient samples compared to normal hematopoietic cells. Likewise, in an analysis of gene expression databases, NLN mRNA was increased in a subset of AML patient samples, compared to normal hematopoietic cells. Next, we assessed the effects of knocking down NLN in AML cell lines (OCI-AML2, NB4, and MV4-11) using three independent shRNAs in lentiviral vectors. Target knockdown was confirmed by immunoblotting. NLN knockdown reduced growth in all three tested cell lines by 50-70%. NLN knockdown also targeted the leukemia initiating cells in vitro and in vivo as NLN knockdown reduced the clonogenic growth of AML cells (40-75%) and the engraftment of TEX cells into immune deficient mice by 85%. Taken together, these data suggest that NLN is necessary for the growth of AML cells. The role of NLN in the mitochondria is not well understood. To gain insight into NLN's mitochondrial function, we investigated NLN's protein interactors using proximity-dependent biotin labeling (BioID). The top hits in the protein-protein interaction screen were mitochondrial matrix proteins and respiratory chain subunits were particularly enriched. Therefore, we measured the effects of NLN knockdown on mitochondrial structure and function. Knockdown of NLN in AML cells reduced basal oxygen consumption without altering reactive oxygen species generation, mitochondrial membrane potential, or mitochondrial mass. No changes were seen in the total levels of respiratory chain complex subunits as measured by immunoblotting on denaturing gels. Respiratory chain complexes assemble into higher order supercomplex structures that maintain the integrity of the mitochondria and promote efficient oxidative metabolism. Therefore, we tested whether NLN is required for the formation of respiratory chain supercomplexes. As measured by blue native polyacrylamide gel electrophoresis, knockdown of NLN impaired the formation of respiratory chain supercomplexes. Through our BioID analysis, we also identified the mitochondrial Ca2+/H+ antiporter, LETM1 (leucine zipper-EF-hand containing transmembrane protein 1) as a top interactor with NLN. LETM1 is a known regulator of respiratory chain supercomplex formation. We showed that knockdown of NLN impaired LETM1 assembly, potentially explaining how NLN regulates supercomplex formation. Finally, we tested if hypoxia influences respiratory chain supercomplex formation and sensitivity to NLN inhibition. OCI-AML2 cells cultured for 72 hours under hypoxic conditions (0.2% O2) showed impaired assembly of respiratory chain supercomplexes, decreased levels of LETM1 protein, and resistance to NLN knockdown. Thus, we discovered that the mitochondrial protease NLN regulates oxidative metabolism by controlling the assembly of respiratory chain supercomplexes. Moreover, we highlight NLN as a potential new therapeutic target for AML. Disclosures Schimmer: Otsuka Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Medivir AB: Research Funding; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees.

Description: Upfront resistance to glucocorticoids (GCs) confers a poor prognosis for children with T-cell acute lymphoblastic leukemia (T-ALL). Using primary diagnostic samples from the Children's Oncology Group trial AALL1231, we previously demonstrated that one-third of patient T-ALL samples are intrinsically resistant to GCs when cultured in the presence of interleukin-7 (IL7), a cytokine that is abundant in the T-ALL microenvironment. Furthermore, we demonstrated that inhibiting JAK/STAT signaling downstream of the IL7 receptor (IL7R) with the JAK1/2 inhibitor ruxolitinib (RUX) overcomes GC resistance in these samples. The objective of the present study was to determine the mechanism of IL7-induced GC resistance in T-ALL and to identify novel therapeutic targets to enhance GC sensitivity. We utilized CCRF-CEM cells, a human T-ALL cell line, as a model system in conjunction with primary patient samples. Exposing CCRF-CEM cells to IL7 induced phosphorylation of STAT5, the predominant downstream effector of IL7R signaling. When cultured in the presence of IL7 and the GC dexamethasone (DEX), CCRF-CEM cells recapitulated the IL7-induced GC resistance phenotype observed in patient samples. This resistance could be overcome with RUX, and Bliss index analysis demonstrated a synergistic relationship between DEX and RUX in the presence of IL7. Furthermore, CRISPR/Cas9 mediated knockout of STAT5 (STAT5 KO) was sufficient to overcome resistance, implicating STAT5 as the critical mediator of IL7-induced GC resistance. DEX exposure potently induced upregulation of IL7R expression in CCRF-CEM cells. Using a luciferase reporter construct containing a series of STAT5 response elements, we demonstrated that in the presence of IL7, DEX-induced upregulation of IL7R expression is associated with increased downstream signal transduction, leading to a significant increase in STAT5 transcriptional output. We then performed RNA-seq to further assess the functional consequences of this enhanced STAT5-mediated transcription. Gene set enrichment analysis (GSEA) revealed that STAT5 target genes were significantly upregulated in cells exposed to DEX and IL7 relative to IL7 alone (normalized enrichment score -2.27; p 〈 0.001; FDR 〈 0.001), suggesting that DEX exposure augments activation of the STAT5 transcriptional program. One critical component of this program that was induced by the combination of DEX and IL7 was the anti-apoptotic family member BCL2, which was not induced by DEX alone. Further analysis of its protein expression in CCRF-CEM cells confirmed this paradoxical upregulation of BCL2 specifically by the combination of DEX and IL7. Furthermore, BCL2 was not upregulated by DEX and IL7 in STAT5 KO cells, consistent with this being a STAT5-mediated effect. IL7-induced GC resistance could be overcome with shRNA-mediated knockdown of BCL2 and with pharmacologic inhibition of BCL2 by venetoclax. Similar to the effect observed with RUX, Bliss index analysis demonstrated synergy between DEX and venetoclax in the presence of IL7. Consistent with our observations in CCRF-CEM cells, an analysis of primary diagnostic T-ALL samples revealed DEX-induced upregulation of IL7R expression in samples with IL7-induced GC resistance, which was associated with increased BCL2 expression in the presence of DEX and IL7. Finally, we performed a similar analysis in healthy murine thymocytes, and found that CD4/CD8 double negative (DN) and CD4 or CD8 single positive (SP) thymocytes, but not double positive (DP) thymocytes, exhibited profound IL7-induced GC resistance that was associated with DEX-induced upregulation of IL7R expression and increased BCL2 expression in the presence of DEX and IL7. These data are consistent with the known role of IL7 specifically at the DN and SP stages of development, and suggests that IL7-induced GC resistance is a physiologic mechanism of GC resistance in normal thymocyte development that is retained during leukemogenesis in a subset of T-ALL samples. Taken together, these data demonstrate that GCs paradoxically induce their own resistance in a subset of T-ALLs and in normal developing T-cells by augmenting a STAT5-mediated pro-survival program that results in upregulation of BCL2. Furthermore, we demonstrate that inhibition of JAK/STAT signaling or of BCL2 may have considerable therapeutic benefit to enhance GC sensitivity in T-ALL patients with IL7-induced GC resistance. Disclosures Teachey: La Roche: Consultancy; Amgen: Consultancy.

Description: Introduction: Currently, patients with refractory Hodgkin lymphoma (HL) or those who relapse multiple times have an extremely poor prognosis. Even patients who do not relapse often experience late toxicities, including secondary cancer, heart failure, pulmonary dysfunction, and infertility. Therefore, new agents and novel therapeutic approaches are urgently needed. Anti-apoptotic proteins such as Bcl-2 and Bcl-xl have been found to be associated with the growth and survival of Hodgkin Reed–Sternberg cells and thus carry the potential to be effective targets for therapeutics. In this study we report the in vitro cytotoxicity, biological correlative findings and drug combination analysis of the novel BH3 mimetic ABT-737 [Abbott laboratories (Abbott Park, IL)] against HL cells. Materials and Methods: HL cell lines (KMH2 and HDLM2) were cultured in the presence of increasing concentrations of ABT-737 or its enantiomer control. Normal bone marrow stromal cells were used as controls for non-specific cytotoxicity. Cell growth inhibition was measured by Alamar blue assay and the induction of apoptosis was demonstrated by an annexin specific staining technique. Time and drug concentration dependent changes in proteins involved in cell survival and apoptosis were investigated by Western blot analysis. The ability of ABT-737 to influence the anti-lymphoma activity of a panel of twenty distinct chemotherapeutic agents was evaluated by drug combination and cell growth inhibition studies. Combination indices (CI) were calculated to identify therapeutic enhancement of different agents in the presence of Bcl-2 inhibition by ABT-737. Results: ABT-737 showed significant dose-dependent cytotoxicity and apoptotic activity against HL cells with an approximate IC50 of 1mM with maximum cell death occurring at about 5mM. At the molecular level, increased levels of cleaved caspase3 and PARP, as well as annexin positivity, were noticeable within three hours of treatment with the agent. Drug combination studies have shown the ability of Bcl-2 inhibition to synergize with novel therapeutic agents that target histone deacetylase function (Apicidin, CI 0.35), Hsp90 stability (17-AAG, CI 0.3) and the activity of specific receptor tyrosine kinases (Sorafenib, CI 0.7 and Sunitinib CI 0.3 for HDLM2 and CI 0.9 for KMH2). Among conventional anti-neoplastic agents, ABT-737 showed significant synergistic activity with irinotecan and oxaliplatin (CI 0.6). Importantly, treatment with ABT-737 decreased the expression of the critical HL cell growth promoter, NF- B as determined by band densities on Western blot analysis: a two fold decrease in KMH2 and a five fold decrease in HDLM2 cells. Specific target modulation was demonstrated by changes in key apoptosis and cell survival regulators such as Bcl-XS/L, Bcl-X, p53 and survivin by two to 10 fold decreases in Western blots. Discussion: Data presented in this study support the hypothesis that Bcl-2 family of proteins can be an effective target for therapeutics in HL. We have shown that the BH3 mimetic ABT-737 induces apoptosis in these cells, characterized by the modulation of key components of cell growth and survival pathways. In addition, we have identified distinct classes of anti-lymphoma and anti-neoplastic agents whose activities are enhanced by concurrent inhibition of Bcl-2. These findings provide the rationale for further evaluation of ABT-737 and the subsequent clinical development of a targeted anti-Bcl-2 therapy for refractory Hodgkin lymphoma.

Description: Introduction: Hodgkin lymphoma (HL) is a common malignancy of children and adolescents and is highly curable with a 5-year overall survival (OS) rate of 〉 97%, yet dose-intensified chemotherapy regimens in combination with radiation therapy come with a high cost in form of long-term toxicity and morbidity (Castellino et al., Blood 2011). This major clinical challenge has resulted in the evaluation of risk-adapted treatment regimens in clinical trials aiming to achieve the optimal equilibrium between high survival rates and prevention of treatment-related toxicity. However, risk stratification is currently limited to the use of clinical factors as there are no validated integral biomarkers that can be employed to either improve risk stratification or as surrogate markers of treatment outcome in pediatric HL. The aim of our study was to perform gene expression profiling (GEP) to uncover disease biology underlying treatment response and develop a prognostic model to tailor first-line therapy in pediatric HL. Methods: We selected 203 formalin-fixed, paraffin-embedded tissue (FFPET) specimens from patients enrolled in a randomized phase 3 clinical trial (AHOD0031) of the Children's Oncology Group (COG) based on the availability of archived FFPET blocks. That trial was designed to assess the value of early chemotherapy response for tailoring subsequent therapy in intermediate-risk pediatric HL. We performed GEP on RNA extracted from pre-treatment FFPET biopsies using NanoString technology and a customized codeset encompassing probes for 784 genes. These genes were either previously reported to be associated with prognosis and outcome in HL or represent the cellular diversity of the tumor microenvironment. Event free survival (EFS) and OS were estimated using the Kaplan-Meier method. Gene expression data were used to develop a predictive model for EFS using penalized Cox regression with parameters trained using leave-one-out cross-validation. Results: Of the 203 tissue samples obtained from the Biopathology Center at the Cooperative Human Tissue Network, 182 (89.7%) passed quality assurance testing, similar to the pass rate achieved for adult HL samples obtained from the Eastern Cooperative Oncology Group trial E2496 (Scott et al., JCO 2013). We applied our previously published 23-gene predictor for OS (Scott et al., JCO 2013), developed using biopsies from adult HL patients to our pediatric cohort. After calibrating the new codeset, 53 patients were classified as "high-risk" and 129 as "low-risk". Importantly, the model failed to predict inferior outcomes in the "high-risk" group (5-year OS 100% vs 95%, log-rank P = 0.125; 5-year EFS 82% vs 70%, log-rank P = 0.159), with patients in the "high risk" group trending to have superior outcomes than the "low risk" patients. Moreover, only 2 genes from this model, IFNG and CXCL11, were significantly associated with EFS in univariate Cox regression analysis (P = 0.003 and 0.048, respectively) but with inverse hazard ratios in the pediatric group compared to adult patients. Therefore, we sought to develop a novel EFS predictive model for pediatric patients treated in the AHOD0031 trial. Using univariate Cox regression we identified 79 genes significantly associated with EFS (raw P 〈 0.05). Using the expression of these 79 genes as the input to penalized Cox regression, we developed a 16-gene model to predict EFS in our training cohort. Using an optimized cut-off for the model score, 31% of patients were designated high-risk and had significantly inferior post-treatment outcome (5-year EFS 38% vs 89%, log-rank P 〈 0.0001). When multivariate analyses were performed including our EFS-model score, disease stage and initial treatment response as variables, only the model score was significantly associated with EFS (P 〈 0.0001, HR 11.3 (95% CI 5.5-23.4)). Conclusions: Failure of the GEP-based model developed in adult HL suggests distinct biology underlies treatment failure in the pediatric age group. We describe the development of a novel predictive model for EFS in intermediate-risk pediatric HL patients that will be validated in an independent cohort of patients treated in the AHOD0031 trial. Successful validation of the model may provide a clinically relevant biomarker for pediatric and adolescent HL patients allowing refinement of risk stratification and the combination of molecular and clinical risk factors at diagnosis. Disclosures Scott: Celgene: Consultancy, Honoraria; NanoString: Patents & Royalties: Inventor on a patent that NanoString has licensed.

Description: Background: Pediatric acute myeloid leukemia (Pedi-AML) accounts for approximately 15% of childhood acute leukemias and the overall survival is 60-70%. Although cytogenetics provides risk stratification, most recurrent genetic events lack agents that specifically target them. Since genetic events are revealed by the expression and activation status of proteins, we hypothesized that we could define recurrent protein expression signatures that could suggest targets for individualized therapies. Methods:Custom Reverse Phase Protein Arrays (RPPA) with 95 Pedi-AML samples and 10 normal CD34+ bone marrow samples were performed and probed with 194 antibodies to determine protein expression levels and activation status. Proteins were divided in protein functional groups (ProFnGrp) to analyze them in the context of other proteins. Progeny clustering was performed to determine the optimal number of protein clusters and principal component analysis was used to visualize the distribution between protein clusters and normal CD34+ cells. Protein networks were generated using known literature associations combined with computational derived edges from the dataset. Associations between clinical features, outcomes and protein clusters were determined. Hierarchical clustering (Figure 1) was performed on a compilation of all protein clusters into one binary matrix to identify recurrent protein expression signatures (PrSIG) that comprised similar combinations of protein constellations(PrCON). A list of proteins that were over or under expressed was made for each signature. Results: For each ProFnGrp 3 to 6 distinct clusters were recognized. All but 2 ProFnGrp (Cell Cycle, Protein Kinase C) had at least one protein cluster that was similar to normal CD34+ samples and all ProFnGrp had clusters specific to the leukemic state. Protein expression levels were overlaid onto the networks and revealed distinct expression and activation states. Hierarchical clustering showed strong co-correlation between protein clusters from various ProFnGrp and suggested 12 PrCON. Patients that expressed similar recurrent combinations of PrCON compiled 8 PrSIG. Heterogeneity was observed for overall survival (OS) and complete remission duration (RD). High OS rates were seen in PrSIG 5 compared to PrSIG 1 (8/12 vs. 3/11 alive, Median NR vs. 54 wks, P=0.09) and high relapse free survival was observed for PrSIG 3 compared to PrSIG 1 (6/6 vs. 3/8 CCR, (Median RD NR vs 39 wks, P=0.04). Rearrangements of 11q23 were overrepresented in PrSIG 2 (7/16, 43.8%) and 7 (5/19, 26.3%) and underrepresented in PrSIG 4 (1/20, 5%) and 6 (0/5, 0%) (P=0.027). Complex karyotype was highly present in PrSIG 8 (4/6, 67%) compared to the overall population (16/95, 16.7%). Hispanic ethnicity was high in PrSig 7 & 8 (53 & 67%) and low in PrSIG 1, 2 4 & 5 (20%, 25%, 5%, 8%). PrSIG membership was also correlated with FAB classification (P=0.025, M0 with PrSIG 4 and M5 with PrSIG 5) as well as with WBC, blast count, HGB and PLT. As we had both Pedi-AML and acute lymphoblastic leukemia (ALL) samples on this RPPA array (see accompanying ALL abstract), this enabled comparison between protein expression levels in both diseases. Combined re-analysis suggested 12 PrSIG and 12 PrCON; most PrSIG and PrCON were dominant for ALL or AML and only 1 PrSIG and 3 PrCON showed overlap between the two diseases. Identification of significantly altered proteins for each PrSIG can be used to select targeted therapies for combination. For example, for PrSIG1 combined inhibition of RPTOR and RICTOR may be useful as both are overexpressed. Conclusion: As hypothesized we demonstrated the existence of protein expression signatures in Pedi-AML based on strong correlations between different protein clusters. Signatures were correlated with therapeutic outcome, as well as with cytogenetics, Hispanic ethnicity, and laboratory features. Recognition of altered proteins within the signatures suggested combinations of targets that could facilitate personalized therapy. Shared protein constellations between AML and ALL indicate joint protein deregulations that could be targetable in both diseases. Figure 1. Hierarchical clustering shows recurrent patterns of 12 PrCON (y-axis) that form 8 recurrent PrSIG (x-axis). The association with Hispanic ethnicity is shown. Figure 1. Hierarchical clustering shows recurrent patterns of 12 PrCON (y-axis) that form 8 recurrent PrSIG (x-axis). The association with Hispanic ethnicity is shown. Disclosures No relevant conflicts of interest to declare.

Description: Although outcomes for patients with T-cell acute lymphoblastic leukemia (T-ALL) have improved dramatically, survival rates for relapsed or refractory T-ALL remain less than 10%. While mechanisms mediating chemotherapy resistance in these patients remain incompletely understood, resistance to glucocorticoids (GC), a central component of therapy, may be particularly important. GC resistance occurs more commonly than resistance to other chemotherapeutic agents in ALL. Additionally, newly diagnosed patients that fail to rapidly clear their peripheral leukemic blasts during an upfront window of prednisone (prednisone poor response) have a poorer outcome, suggesting differences in GC sensitivity may exist at diagnosis. Here, we develop an in vitro assay to model the early prednisone response. Using primary, pre-treatment human T-ALL samples, we demonstrate that individual T-ALLs have distinct intrinsic GC sensitivity thresholds at diagnosis and that this threshold can predict end induction MRD. To interrogate potential mechanisms of GC resistance, we use a panel of patient-derived xenografts (PDX) generated from diagnostic T-ALLs. We find that intrinsic GC resistance is uniformly seen in T-ALLs that arise at the early thymic progenitor (ETP) stage as well as in a subset of non-ETP T-ALLs. Removal of IL7 from the media or inhibition of IL7/JAK/STAT signaling with the JAK1/2 inhibitor ruxolitinib or a novel JAK3 inhibitor, JAK3i, reverses GC resistance in ETP and a subset of the non-ETP T-ALL. This effect is drug specific, since IL7 does not offer protection from death induced by other agents. IL7-dependent GC resistance can be predicted by hyper-responsiveness to IL7 stimulation. Mechanistically, the combination of dexamethasone and ruxolitinib alters the balance between BCL2 and BIM in IL7-dependent, but not IL7-independent, GC resistant T-ALL samples. Together, these data support a model where IL7, a cytokine with leukemogenic properties that is normally present in lymphopoietic niches, contributes to intrinsic GC resistance in a subset of T-ALL samples. This environmentally induced GC resistance may be reversed with IL7/JAK/STAT pathway inhibition. This could result in an augmented leukemotoxic effect of GC treatment, potentially enhancing efficacy of glucocorticoids in a subset of patients and justifying exposure to the toxic side effects of GCs. Disclosures Taunton: Global Blood Therapeutics: Equity Ownership; Kezar Life Sciences: Equity Ownership, Research Funding; Pfizer: Research Funding; Principia Biopharma: Consultancy, Equity Ownership; Circle Pharma: Consultancy, Equity Ownership; Cell Design Labs: Consultancy, Equity Ownership. Wood:Juno: Other: Laboratory Services Agreement; Amgen: Honoraria, Other: Laboratory Services Agreement; Pfizer: Honoraria, Other: Laboratory Services Agreement; Seattle Genetics: Honoraria, Other: Laboratory Services Agreement. Teachey:Novartis: Research Funding.

Description: Introduction: Acute myeloid leukemia (AML) comprises about 18% of childhood leukemias, with an incidence of 7.7 cases per million in the United States. The evidence for variation in disease distribution by race and ethnicity is limited, although there is a slight increased risk for the promyelocytic subtype in Hispanics (Puumala et al, Pediatr Blood Cancer, 2014). In earlier treatment eras (pre-2002), the Children's Cancer Group reported Hispanics with AML to have inferior overall survival (OS) when compared with non-Hispanics (Lange et al, Blood, 2008; Aplenc et al, Blood, 2006), but their event-free survival did not differ significantly. According to recent SEER data, both Hispanic children and adults with AML demonstrated similar OS disparities (Hossain et al, Cancer Epidemiol, 2015; Patel et al, Am J of Clin Oncol, 2015), despite the fact that age at presentation and cytogenetic features were more favorable in Hispanics compared with non-Hispanics. In order to better understand the impact of Hispanic ethnicity upon AML outcomes, we examined relapse-free survival (RFS) and OS in children diagnosed with AML at Texas Children's Hospital (TCH), which has a large Hispanic population, and compared host, disease, and treatment factors that may have affected outcomes. Methods: We retrospectively reviewed medical records from children (age 0-21 years) with newly diagnosed AML treated at TCH between 1998 and 2015. Subjects with acute promyelocytic leukemia or therapy-related AML were excluded. Self-reported race and ethnicity were used to categorize the study population into Hispanics (of any race) and non-Hispanics. Differences in proportions of host, disease, and treatment characteristics between the two groups were compared using Pearson's X2 test. The Kaplan-Meier method was applied to estimate RFS and OS. We then used the Wilcoxon-Breslow-Gehan test to determine if survival functions (RFS and OS) were statistically different by ethnicity, adjusting for treatment era (pre-vs, post 2002). RFS was defined as time from the date of diagnosis until date of relapse. Patients without an event were censored at the date of last known contact. Research was performed under a local Institutional Review Board-approved protocol and in accord with the Declaration of Helsinki. Results: Of the 99 AML cases with available clinical information, 37 (37%) self-identified as Hispanic. Host, disease, and treatment factors in Hispanic and non-Hispanic subjects with AML did not differ according to prognostic factors such as age at diagnosis or favorable cytogenetic features (Table 1). Additionally, Hispanics and non-Hispanics did not differ significantly in cause of death (disease-related or other). The groups did not differ significantly in OS, but Hispanics had significantly poorer RFS (p=0.03) (Figure 1). Conclusions: Despite no significant differences in frequency of known AML risk factors, the TCH Hispanic population was both significantly more likely to relapse and had an earlier time to relapse than did non-Hispanics. This effect was even more surprising given that this population was twice as likely to have AML characterized by favorable cytogenetic features, although this enrichment did not reach significance. Of note, the RFS difference we observed is unlikely to be related to treatment compliance or socioeconomic factors, as all AML patients were hospitalized throughout treatment. Further study is needed to confirm this finding in a larger pediatric AML cohort, and to identify host factors related to Hispanic ancestry that may be responsible for the differences observed in RFS. Figure 1. Patient characteristics *Number of subjects in each category is shown in parentheses unless otherwise specified. SD=Standard deviation, CBF = core binding factor, MRD = minimal residual disease, BMT = bone marrow transplant Figure 1. Patient characteristics. / *Number of subjects in each category is shown in parentheses unless otherwise specified. / SD=Standard deviation, CBF = core binding factor, MRD = minimal residual disease, BMT = bone marrow transplant Figure 2. Comparison of AML relapse-free survival in Hispanics vs. non-Hispanics, adjusted for treatment era Figure 2. Comparison of AML relapse-free survival in Hispanics vs. non-Hispanics, adjusted for treatment era Disclosures No relevant conflicts of interest to declare.